This proposal builds on extensive literature that implicates aberrant regulation of amyloid precursor protein (APP) processing and Abeta production as a major cause of Alzheimer's disease, and the APP intracellular domain (AICD) as a central player in this process. Recent results from our labs show that the prolyl isomerase Pin1 catalyzes cis/trans isomerization of the phosphorylated (p) T668P motif of APP and regulates APP processing and Abeta production. We propose a set of synergistic experiments to address the structural and dynamic mechanisms by which Pin1 regulates the conformation and processing of APP in vitro and in vivo. In Aim 1 we will apply NMR dynamics methods to determine the structural, microscopic kinetic and thermodynamic, and NH-bond dynamic parameters that describe Pin1-catalysis of phosphorylated AICD. The overall goal of Aim 1 is to derive NMR-based mechanistic models for functional motions in Pin1, and to predict mutations to test these models. In Aim 2 we will make these NMR-predicted mutants and evaluate their effects on APP processing and Abeta production in vitro and in vivo. The overall goal of Aim 2 is to validate NMR-derived models for the catalytic mechanism and for functional motions. In Aim 3 we will randomly mutagenize the Pin1 WW domain and select for mutants with high cis-isomer affinity. The effects of the selected mutants on APP processing and Abeta production will be tested in vitro and in vivo. The overall goal of Aim 3 is to determine the role(s) of isomer-specific recognition of the pT668P AICD motif in APP processing and Abeta production. Overall, we will extend our limited structure-based understanding of Pin1 function, exploring functional motions by comparing measured microscopic and NH- bond specific rates in Pin1. Motional models will be tested in vitro and in vivo using all available technology, including the effects on APP processing and Abeta production. By elucidating the regulation of the cis and trans isomers of pT668-APP and establishing their roles in APP processing and Abeta production, these studies will potentially open new avenues for development of novel Alzheimer's disease therapeutics. In lay language, we have recently identified a new enzyme important for the development of Alzheimer's disease. In this proposal, we will combine NMR dynamics, cellular and molecular biology approaches to study how this enzyme affects Alzheimer's disease processes and hope to eventually identify new therapeutic targets.